Electric lamp



Patented Nov. 7, 1939 UNITED STATES PATENT OFFICE '7 Claims.

This invention relates to incandescent lamps and in one aspect consists in a filament of novel construction designed to provide a light source of highly concentrated brilliancy with asmall spread between the leads and which is soshaped within the bulb in which the light source is to be located. In another aspect the invention consists in the combination with a reflecting lamp of a filament having a plurality of parts or branches disposed side by side and connected in series by diagonal cross-over connections.

My invention solves many serious difficulties which arise in the construction and maintenance of reflecting incandescent lamps, particularly those of high wattage. In the first place it is desirable to concentrate the filament so as to locate it with the greatest possible exactitude at or near the focus of the reflecting surface. Heretofore this has required that the leads be located so close together as to create danger of arcing between the leads or between adjacent parts of the filament itself. The practical effect of this difiiculty has been to limit reflecting electric lamps in their eificiency.

In accordance with the present invention, however, I am able to maintain a relatively low voltage drop between the leads and between adjacent parts of the filament and still employ a filament arranged in a concentrated pattern, of high wattage and with maximum clearancebetween the filament and the reflecting coating of the lamp. These desirable results are secured by employing a coiled coil filament having spaced loops or branches arranged in series and cross-connected between theirdiametrically opposite ends-or intermediate points. For example, I may arrange the filament in two V-shaped branches disposed side by side and parallel to each other, supporting one diametrically opposite pair of ends by the lead-in wires and the other pair of ends by supporting wires which are cross-connected by a diagonal connector.

the filament pattern, the potential drop through each branch of the filament comprises only onehalf of thetotal drop through the filament, and

Thus the full potential drop occursv across the maximum diametrical dimension of where exceeds one-half the total potential drop of the filament.

An important advantage of this arrangement of the filament branches and their cross-over connections is. that the current in any adjacent branches is in the same direction, with the result that the induced electro-magnetic field surrounding each branch is similar in character and electron flow between them is deflected. This reduces or counteracts the tendency of arcing, particularly in a gas-filled lamp, and so increases the life of the lamp and permits employing a more compact filament design than would be possibleif the current flow were in opposite directions, under which conditions of course, the electron flow between the branches would be stimulated and increased with a corresponding increase in the tendency to arc.

An important field of use of my invention is in lamps in which a portion of the bulb or reflector has the shape of a parabola expanded until its focal point constitutes a ring of substantial diameter. Theoretically the most efiicient results are obtained by locating the filament so that it coincides with the focal ring of the parabolic refiector. As herein shown, however, the branches of the filament are located symmetrically in the bulb and so that they intersect and occupy a portion of the focal plane of the lamp. This ex- .tremely concentrated light source is thus disposed to the best possible advantage with respect to the focus or focal zone of the lamp.

Whilel have referred to a filament comprising two branches it is entirely practical to arrange the filament in three or more branches connected in series or in series-parallel and arranged so that the potential drop through the system is dist-ributed in the manner already explained. These branches of the filament may be disposed in a single plane or corresponding branches may be lobated in intersecting planes or the branches may be located at different levels, all as in accordance with the requirements of the service under consideration.

Another feature of the invention consists in a fuse or fuses provided in circuit between two of the filament branches or lead-in wire sections. Lamps of the general type to which this invention relates have sometimes exploded when burned to near the end .of their normal life due to the failure of the filament and the formation oran arc drawing an excessive amount of current and generating intense heat in the bulb. The diagonal crossconnection which I is characteristic of my novel filament supplies a convenient location for a fuse fore results from this characteristic of my novel filament.

These and other features of the invention will be best understood and appreciated from the following description of a preferred embodiment thereof, selected for purposes of illustration'and shown in the accompanying drawing in which,

Fig. 1 is a view in elevation of an incandescent lamp, portions being broken away to expose the filament,

Fig. 2 is a wiring diagram of the filament cir-- cuit,

Fig. 3 is a view in perspective of the filament and its supports, I

Fig. 4 is a wiring diagram of a three-branch filament, and

Fig. 5 is a fragmentary view of a coiled filament wound upon a rectangular core.

While the filament of my invention is in no sense limited to use in a refiectinglamp, I have shown such a filament in Fig. l as embodied in a reflecting lamp of,the type dlsclosedin the U. S. Letters Patent No. 2,110,590. The bulb includes a rounded end portion In which is clearf and which transmits the beam of the lamp. This merges into the parabolic portion H which. in turn merges in the enlarged globular portion I2, and this into the neck E3. The portion I l is a parabola of revolution expanded laterally until its focal point described a circle of substantial diameter or a focal ring and it is in this ring that the light source should be located for best optical results. The parabolic portion H mergesinto a bulging portion l2 which enlarges the bulb in the vicinity of its light source. The neck l3 terminates in a metal base ll of usual construction. The lamp is provided with an internal coating of silver or other reflecting medium which extends substantially from its line of maximum diameter to a line in the neck of the bulb and has the efiect of concentrating all. the light of the lamp generated in the lamp.

The filament, shown in the lamp of Fig. 1 as constituting one desirable embodiment of the invention, comprises two coiled coil filament branches or sections 2| and 22. The filament is disposed with corresponding branches in parallel relation, that is, the axes of the'each pair of branches lie in intersecting planes. The general location of the filament branchescoincides as nearly as possible with the focal ring of the reflecting surface and they are symmetrically disposed with respect to its plane, that is, the apex of the filament branches 2| and 22 projects above the plane of the focal ring about as much as the outerends of the filament branches extend below it. The lead wires]? and I8 sealed in the press of the mount l5 project upwardly and supportdiag onally opposite ends of the branches 2! and 22. In Fig. 2 the lead wire I! is shown as connected to the left end of the branch 2! and the o lead wire l8 as connected to the right end of the branch 22. The other ends of the filament branches are positioned by supporting wires l9 and 20 as best shown in Figs. 2 and 3. From this it will appear that the lead wires l1 and 18 are spaced from each other by the maximum dimension of the filament pattern, that is to say, by a diagonal of the rectangle formed by projecting the filament on a plane. The supporting wires [9 and 20 are located at the ends of the other diagonal of this plane pattern. The filament sections are connected in series by a diagonal crossover wire 25 extending between the supporting wires l9 and 20 at a substantial distance below the coils of the filament. As a result of these connections it will be noted that when the lamp is energized current will flow in the same direction simultaneously in both its sections. Additional supporting wires 23 and 24, which are also sealed in the press of the mount l5, or secured to the disk l6, serve to support the centers of the two filament loops or branches 2| and 22 and are spaced apart from the wire .25.

Referring more particularly to the diagram of Fig. 2 it will be seen that the full voltage drop of the circuit, which may be 120v0lts, occurs between the lead-in wires l] and [8; which are spaced by the'maximum distanc'e pe'rinitted in the filament pattern, A voltagefdropoffid'yolts occurs between the two ends'of eac 'of the filament branches, and avoltage'dro ""0 $30 volts-occurs between adjacent ends of the sult is that at no place in the filani'enfip'atte'rn is there a maximum drop of potential across a gap sufiiciently narrow to invite arcing." A fuse 26 may be and is herein shown as being inserted in the cross-over connection 25, and is thus interposed in series circuit between the two branches of the filament.

In Fig. 4 is shown the wiring diagram of a filament divided into three branches 30. In this arrangement the lead-in wires 21 and 28 are located at the diagonally opposite corners of the pattern and support wires 29 carry opposite ends of the outer filament branches and both ends of the intermediate filament branch. Each of the outer filament branches is connected at one end to the intermediate branch by the diagonal cross-over connections 3|. One of these is provided with a fuse 32 which is thus directly interposed in series between two of the filament branches. The potential distribution is indicated in Fig. 4, there being a drop of 40 volts through each filament branch and 40 volts between adjacent ends of the respective branches. ready explained tends to prevent arcing between the lead wires or between any adjacent portions of the filament.

In Fig. 5 is indicated a shape of filament coil which may be advantageously employed in a lamp having a reflecting disk such as the disk I6 shown in Fig. 1 and in the same position occupied by the filament branches in Fig. 1. The coil may be formed by winding the coiled coil filament 36 upon an oblong mandrel 35 and in'the lamp the coil is disposed in the relation to the reflecting disk suggested by Fig. 5, that is to say, with the major cross-sectional axis of the core perpendicular to the disk. The reason for this is that the disk I 6 tends to'become more discolored by the deposition of tungsten vapor than the refiecting coating of the walls of thebulb. By disposing the filament as suggested in Fig. 5 a smaller part of. the emitted light is directed to the disk than to the reflecting walls of the bulb.

This arrangement as al- The rectangular section filament may be advantageously employed in lamps having no reflecting disk; where it is desired to direct more light rays into certain selected directions. and

5 especially in lamps assembled with external reflectors defining a focus or. a focal zone within the bulb in which the light source is to be located. For example, in a lamp having a parabolic refiecting surface a rectangular section filament maybe located with its major axis parallel to the axis of the parabola.

-WhileI have shownin thedrawing filaments having branches which comprise each a simple coil, it is contemplated that a series-parallel arrangement of branches may be employed, that is to say, an arrangement in which each branch comprises a pair of coils connected in parallel and each pair connected in series. In my prior application. Serial No. 15,605, filed April 10, 1935,

go I have disclosed several forms of coiled coil filaments which may be utilized to good advantage in connection with the present invention.

The reflecting coating may be applied to the bulb internally or externally as desired, although the present invention is particularly useful in connection with internally silvered bulbs because it facilitates the provision of ample space between the concentrated filament and the silver coating.

. thus avoiding overheating of the silver.

In some cases, for example in lamps designed to operate on a 220 volt circuit. it may be desirable to employ two or more fuses in the filament assembly. Accordingly a fuse may be provided in each of the designed cromver connections or lead-in wires.

Having thus disclosed my invention and described several embodiments thereof for illustrative purposes, but not in a limiting sense, what I claim as new and desire to receive as Letters Patent is: p

- 1. An electric lamp comprising a bulb, a filament having a plurality of parts spaced laterally from each other, arranged electrically in series and havingadiagonal cross connection which uincludesafuse.

2. An electric lamp comprising a bulb, a filament therein having "a plurality of distinct sections arranged electrically in series, and a fuse disposed in circuit between two of the filament sections. 5

3. An electric lamp comprising a bulb, a filament therein having two sections of coiled coil wire disposed in substantially parallelrelation and disposed in series with a diagonal cross connection between them, and a fuse also disposed 10 between them. 7

4. An electric lamp comprising a bulb, lead wires and supporting wires projecting upwardly intothe bulb in a four-cornered pattern, two upwardly directed V-shaped sections of filament 10- u cated above the ends of the lead and supporting wires in substantially parallel relation, the lead wires being connected to the filament sections at .di'agonaliy opposite ends, and'a diagonal cross connection between the supporting wires located go below the filament sections and including a fuse therein.

5. An electric la'mp comprising a bulb having a reflecting disk in its neck portion, and a coiled coil filament having -a substantially rectangular 2g coil section disposed with its major axis directed toward said reflecting disk.

6. An electric lamp comprising a bulb having a. reflecting coating upon its side walls. and a. coiled coil filament having a substantially, oblong 3o coil section disposed with its larger surfaces facing said reflecting coating.

7. A gas-filled electric lamp including in its structure a bulb. and a light source enclosed therein and comprising a plurality of distinct 5 coiled coil filament loops, means for supporting the ends and the centers of the loops in the bulb so that the loops are maintained in parallel relationship, and an electrical cross-over connection between diametrically opposite ends of ada jacent loops connected to said end supporting means and remote from the supports for the loop centers and from the ends of the loops.

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